Method for measuring impurity contents in poly-l-lactic acid and use

Abstract

The present invention relates to the technical field of measurement. Disclosed are a method for measuring impurity contents in poly-L-lactic acid and a use. The method comprises: dissolving a poly-L-lactic acid sample in dichloromethane and adjusting same to a fixed volume to prepare a test solution; and injecting the test solution into a gas chromatograph, recoding a chromatogram, and computing the contents of dodecanol and 2-ethylhexanoic acid by means of an external standard method. The method for measuring impurity contents in poly-L-lactic acid provided in the present invention allows for simultaneous measurement of two impurities, i.e., dodecanol and 2-ethylhexanoic acid, achieves good separation degrees on the two impurities, is simple to operate, and achieves high specificity, high sensitivity, high accuracy, high reproducibility, and high durability; the retention times of chromatographic peaks of substances to be measured are appropriate, and impurities are quantified by using an external standard method, the measurement results are accurate and reliable, and both dodecanol and 2-ethylhexanoic acid can be effectively measured, thereby providing a basis for quality control of poly-L-lactic acid.

Description

A method for detecting impurities in poly-L-lactic acid and its application Technical Field

[0001] This invention belongs to the field of impurity content detection technology, specifically relating to a method and application for detecting impurity content in poly-L-lactic acid. Background Technology

[0002] With the continuous development of society and economy and the sustained growth of the global population, Earth's resources have been severely exploited, and environmental and energy problems such as global warming and the depletion of oil resources are becoming increasingly severe. Among these, the pollution caused by polymeric compounds synthesized from resources such as petroleum during production, consumption, and disposal is becoming increasingly prominent, highlighting the importance of environmental protection. Therefore, in recent years, non-petroleum-based biodegradable materials have received increasing attention. Among numerous biodegradable materials, poly-L-lactic acid (PLA), as a novel environmentally friendly polymer, has gradually gained popularity. PLA is a polymer material synthesized from small-molecule L-lactic acid produced by microbial fermentation of biomass raw materials (cassava, beets, sugarcane, straw cellulose, etc.). As a biodegradable material, it can replace current non-degradable plastics, greatly reducing plastic pollution and better aligning with the concepts of circular economy and sustainable development. It can fundamentally solve the problem of rising chemical raw material costs caused by the depletion of oil resources and soaring oil prices. Furthermore, PLA has good thermal processability, biocompatibility, and degradability, and will not cause environmental pollution after use. Its physical and mechanical properties are easily adjustable, allowing it to replace many traditional petroleum-based plastics and find wide application in numerous fields such as clothing, packaging, agriculture, automobiles, electronics, and biomedicine. In today's world of increasingly scarce petroleum resources and severe environmental pollution, poly-L-lactic acid (PLA) perfectly meets people's pursuit of a natural, green, and environmentally friendly lifestyle.

[0003] Currently, there are two main methods for synthesizing poly-L-lactic acid (PLA): direct polycondensation and ring-opening polycondensation. Direct polycondensation is simpler but generally only yields oligomers; ring-opening polycondensation is more complex and costly but can produce high molecular weight PLA. The ring-opening polymerization method for preparing PLA uses L-lactic acid as a raw material, stannous octoate as a catalyst, and dodecanol as a capping agent. The specific reaction formula is as follows:

[0004]

[0005] Studies have shown that dodecanol has a certain impact on the thermal stability of poly-L-lactic acid (PLA), promoting its degradation and reducing its thermal stability. Unreacted dodecanol can also react with stannous octoate at high temperatures to produce the byproduct 2-ethylhexanoic acid. 2-Ethylhexanoic acid is a chemical substance that irritates the skin and mucous membranes. Since PLA is used in clothing, packaging, and biomedicine, the residual amount of 2-ethylhexanoic acid in products should be strictly controlled. To improve the thermal stability and safety of PLA and control the product quality of PLA raw materials, controlling the residual amounts of dodecanol and 2-ethylhexanoic acid is crucial.

[0006] The study on residual amounts of end-capping agents in biodegradable polylactic acid materials (Biomedical Engineering Research, 2015, 34(2): 106-109) discloses a quantitative method for detecting the residual amount of dodecanol, the end-capping agent in polylactic acid, using gas chromatography. The chromatographic conditions were: DB-624 capillary column, programmed temperature rise (initial temperature 60℃, maintained for 3 minutes, then increased to 250℃ at a rate of 30℃ per minute, maintained for 10 minutes); injection port 250℃; detector 260℃; split ratio 10:1; injection volume 2μl; carrier gas flow rate 3.0ml / min. The preparation method for the test sample was as follows: 1g of polylactic acid was dissolved in 5ml of chloroform, methanol was slowly added dropwise to precipitate the polylactic acid, and the volume was adjusted to 25ml with methanol. The sample was then centrifuged at 3000 rpm for 20 minutes. However, this method could not completely separate dodecanol and 2-ethylhexanoic acid, and the chromatographic conditions were not suitable for the simultaneous detection of dodecanol and 2-ethylhexanoic acid. Furthermore, the above-mentioned test sample solution preparation method uses chloroform, a Class II precursor chemical. Due to its potential toxicity and environmental impact, its use and management are highly risky. The test sample preparation process is cumbersome and prone to experimental deviations.

[0007] Therefore, establishing a simple and practical analytical method to determine the residual amounts of dodecanol and 2-ethylhexanoic acid in poly-L-lactic acid is essential for the research and development and production process control of poly-L-lactic acid. Summary of the Invention

[0008] To address the problems of existing technologies that cannot simultaneously detect the residual amounts of dodecanol and 2-ethylhexanoic acid in poly-L-lactic acid and that the preparation methods for the test solution are complex, this invention provides a method and application for detecting the impurity content in poly-L-lactic acid. This method has good specificity, high sensitivity, high accuracy, good reproducibility and robustness, and can be used to control the residual amounts of dodecanol and 2-ethylhexanoic acid in poly-L-lactic acid.

[0009] This invention is achieved through the following technical solution:

[0010] A method for detecting the content of impurities in poly-L-lactic acid, wherein the impurities are dodecanol and 2-ethylhexanoic acid;

[0011] The method for detecting impurities in poly-L-lactic acid includes the following steps:

[0012] (1) Preparation of test solution: The poly-L-lactic acid sample was dissolved in dichloromethane and diluted to volume to prepare the test solution;

[0013] (2) Gas chromatography detection: Inject the test solution from step (1) into the gas chromatograph, record the chromatogram, and calculate the content of dodecanol and 2-ethylhexanoic acid according to the external standard method.

[0014] Further, in step (1), each 1 ml of the test solution contains 9-11 mg of poly-L-lactic acid sample.

[0015] Furthermore, the detection conditions for the gas chromatography are as follows: the chromatographic column is a capillary column with polyethylene glycol as the stationary phase; the column temperature is 135~155℃; the carrier gas is nitrogen, and the flow rate is 0.7~0.9 ml / min; the injection port temperature is 240~260°C; the detector temperature is 270~290°C; the injection method is split injection with a split ratio of 10:1, and the injection port pressure is 75 kPa.

[0016] Furthermore, the chromatographic column is a DB-WAX, 30m × 0.32mm, 0.5μm.

[0017] Furthermore, in step (2), the injection volume into the gas chromatograph is 1.0 μL.

[0018] In this invention, the method for detecting the impurity content in poly-L-lactic acid is applied in evaluating the quality of poly-L-lactic acid. Beneficial effects

[0019] The method for detecting impurities in poly-L-lactic acid provided by this invention can simultaneously detect two impurities, dodecanol and 2-ethylhexanoic acid, with good separation between the two impurities and simple operation. This method has good specificity, high sensitivity, high accuracy, good reproducibility and robustness, and the retention time of the chromatographic peak of the analyte is appropriate. The external standard method is used to quantify the impurities, and the detection results are accurate and reliable. Both dodecanol and 2-ethylhexanoic acid can be effectively detected, providing a basis for the quality control of poly-L-lactic acid. Attached Figure Description

[0020] Figure 1 shows the gas chromatogram of the specificity test; where (A) dichloromethane, (B) dodecanol positioning solution, (C) 2-ethylhexanoic acid positioning solution, (D) reference solution, and (E) test solution;

[0021] Figure 2 shows the gas chromatograms of the reference solution at different column temperatures, where (A) is 145℃, (B) is 135℃, and (C) is 155℃.

[0022] Figure 3 shows the gas chromatograms of the reference solution at different detector temperatures, where (A) is 280℃, (B) is 270℃, and (C) is 290℃.

[0023] Figure 4 shows the gas chromatograms of the reference solution at different injection port temperatures, where (A) 250℃, (B) 240℃, and (C) 260℃.

[0024] Figure 5 shows the gas chromatograms of the reference solution under different column conditions, where (A) is column serial number USF217243H and (B) is column serial number USD118225H.

[0025] Figure 6 shows the gas chromatogram of the reference solution of Comparative Example 1. Detailed Implementation

[0026] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0027] In the following examples, the batch number of the dodecanol standard was 2023090201, with a content of 99.0%, and it was produced by Shanghai Aladdin Biochemical Technology Co., Ltd.; the batch number of the 2-ethylhexanoic acid standard was 2023091502, with a content of 99.0%, and it was produced by Shanghai Maclean Biochemical Technology Co., Ltd.; and the batch number of the poly-L-lactic acid sample was 23003F006, and it was produced by Shandong Caicai Medical Technology Co., Ltd.

[0028] Example 1

[0029] (1) Preparation of positioning solution:

[0030] Dodecyl alcohol positioning solution: Accurately weigh dodecyl alcohol standard, and quantitatively dilute with dichloromethane to prepare a dodecyl alcohol positioning solution containing 15 μg dodecyl alcohol per 1 ml;

[0031] 2-Ethylhexanoic acid positioning solution: Accurately weigh 2-ethylhexanoic acid standard, and quantitatively dilute with dichloromethane to prepare a 2-ethylhexanoic acid positioning solution containing 15 μg of 2-ethylhexanoic acid per 1 ml;

[0032] (2) Preparation of reference solution: Accurately weigh dodecanol and 2-ethylhexanoic acid, and quantitatively dilute with dichloromethane to prepare a mixed solution of 2-ethylhexanoic acid containing 15 μg dodecanol and 15 μg 2-ethylhexanoic acid per ml;

[0033] (3) Preparation of test solution: Accurately weigh the poly-L-lactic acid sample, dissolve it in dichloromethane and quantitatively dilute it to prepare a test solution containing 10 mg of poly-L-lactic acid sample per 1 ml.

[0034] Example 2

[0035] Specificity test:

[0036] The dodecanol positioning solution, 2-ethylhexanoic acid positioning solution, reference solution, test solution, and dichloromethane solvent prepared in Example 1 were injected into a gas chromatograph. The chromatographic conditions were as follows: the column was a capillary column (DB-WAX, 30m × 0.32mm, 0.5μm) with polyethylene glycol as the stationary phase (USF217243H); the column temperature was 145℃; the carrier gas was nitrogen, with a flow rate of 0.8ml / min; the injection port temperature was 250°C; the detector temperature was 280°C; the injection method was split injection with a split ratio of 10:1; the injection port pressure was 75kPa; and the injection volume was 1.0μL. The resulting chromatogram is shown in Figure 1, where A, B, C, D, and E are the chromatograms of dichloromethane, dodecanol positioning solution, 2-ethylhexanoic acid positioning solution, reference solution, and test solution, respectively.

[0037] The retention time, theoretical plate number, and resolution are shown in Table 1 below:

[0038] Table 1 Results of specificity test

[0039]

[0040] As shown in Table 1 and Figure 1, the blank solvent does not affect the detection of dodecanol and 2-ethylhexanoic acid in the poly-L-lactic acid sample, and the resolution between dodecanol and 2-ethylhexanoic acid is 4.3, with theoretical plate numbers greater than 5000, indicating that the method of the present invention has good specificity.

[0041] Example 3

[0042] Limit of Quantification and Limit of Detection Test

[0043] The dodecanol and 2-ethylhexanoic acid positioning solutions from Example 1 were stepwise diluted and subjected to gas chromatography detection under the same chromatographic conditions as in Example 2. The limit of quantitation was determined when the signal-to-noise ratio was approximately 10:1, and the limit of detection was determined when the signal-to-noise ratio was approximately 3:1, thus validating the method sensitivity. The results are shown in Table 2.

[0044] Table 2 Results of tests for limit of quantitation and limit of detection

[0045]

[0046] As shown in Table 2, the method of the present invention has good sensitivity and can meet the detection requirements.

[0047] Example 4

[0048] Linearity test

[0049] The dodecanol positioning solution and 2-ethylhexanoic acid positioning solution from Example 1 were taken and diluted to different concentrations to prepare linear relationship solutions of different concentrations. Gas chromatography was performed for detection under the same chromatographic conditions as in Example 2. The linear relationship equation was calculated, and the results are shown in Table 3.

[0050] Table 3. Results of linear relationship experiments

[0051] As shown in Table 3, dodecanol and 2-ethylhexanoic acid exhibit good linearity within the range of the limit of quantitation to 150% of the limit concentration, with correlation coefficients greater than 0.999.

[0052] Example 5

[0053] System precision test

[0054] The reference solution prepared in Example 1 was subjected to gas chromatography detection. Six consecutive injections were performed under the same chromatographic conditions as in Example 2. The peak areas and retention times of dodecanol and 2-ethylhexanoic acid were statistically analyzed, and the RSD (%) was calculated to examine the system precision. The experimental results are shown in Table 4.

[0055] Table 4 System precision test results

[0056]

[0057] As shown in Table 4, the RSD (%) of peak area and retention time of the reference solution was less than 2% after six consecutive injections, indicating that the system precision of the method of the present invention is good.

[0058] Example 6

[0059] Accuracy (recovery rate) test:

[0060] (1) Reference stock solution: Weigh appropriate amounts of dodecanol and 2-ethylhexanoic acid accurately, place them in the same volumetric flask, and dilute quantitatively with dichloromethane to prepare a reference stock solution containing 150 μg dodecanol and 150 μg 2-ethylhexanoic acid per ml.

[0061] (2) Reference solution: Accurately measure 1 ml of the reference stock solution, place it in a 10 ml volumetric flask, dilute with dichloromethane to the mark, and shake well to obtain the reference solution;

[0062] (3) 50% recovery solution: Take 100 mg of poly-L-lactic acid sample, accurately weigh it, put it in a 10 ml volumetric flask, add 0.5 ml of reference stock solution, then add dichloromethane to dissolve and dilute to the mark, shake well, and prepare 3 parallel portions;

[0063] (4) 100% recovery solution: Weigh 100 mg of poly-L-lactic acid sample accurately, place it in a 10 ml volumetric flask, add 1.0 ml of reference stock solution, then add dichloromethane to dissolve and dilute to the mark, shake well, and prepare 3 parallel portions.

[0064] (5) 150% recovery solution: Weigh 100 mg of poly-L-lactic acid sample accurately, place it in a 10 ml volumetric flask, add 1.5 ml of reference stock solution, then add dichloromethane to dissolve and dilute to the mark, shake well, and prepare 3 parallel portions.

[0065] The above solution was subjected to gas chromatography under the same chromatographic conditions as in Example 2. The external standard method was used to calculate the impurity recovery rate and to examine the accuracy of the method. The experimental results are shown in Table 5.

[0066] Table 5 Accuracy Test Results

[0067]

[0068] As shown in Table 5, the recovery rate of each impurity at different concentrations using the method of the present invention is in the range of 80% to 110%, and the RSD (%) of the recovery rate of each impurity is in the range of 10%. The method has good accuracy, and the results of impurity detection are accurate and reliable.

[0069] Example 7

[0070] Durability test

[0071] The robustness of the method was examined by varying the column temperature, detector temperature, injection port temperature, and chromatographic columns (different serial numbers), using the resolution of the reference solution prepared in Example 1 as an indicator. Gas chromatograms of the reference solution at different column temperatures are shown in Figure 2, where (A) is 145℃, (B) is 135℃, and (C) is 155℃; gas chromatograms of the reference solution at different detector temperatures are shown in Figure 3, where (A) is 280℃, (B) is 270℃, and (C) is 290℃; gas chromatograms of the reference solution at different injection port temperatures are shown in Figure 4, where (A) is 250℃, (B) is 240℃, and (C) is 260℃; gas chromatograms of the reference solution under different column conditions are shown in Figure 5, where (A) is column serial number USF217243H and (B) is column serial number USD118225H; the resolution results are shown in Table 6 below.

[0072] Table 6 Durability Test Results

[0073]

[0074] As shown in Figures 2-5 and Table 6, by changing the chromatographic conditions of the present invention, the resolution between each component in the mixed solution is greater than 3.0, and the method has good robustness.

[0075] Comparative Example 1

[0076] (1) Preparation of reference solution: Take appropriate amounts of dodecanol and 2-ethylhexanoic acid, and dilute them quantitatively with methanol to prepare a reference solution containing 15 μg dodecanol and 15 μg 2-ethylhexanoic acid per ml;

[0077] (2) Gas chromatography detection, chromatographic conditions: capillary column (DB-624, 30m×0.32mm, 1.8μm) with (6%)cyanopropylphenyl-(94%)dimethylpolysiloxane as stationary phase, temperature program (initial temperature 60℃, maintained for 3 minutes, then increased to 250℃ at a rate of 30℃ per minute, maintained for 10 minutes); injection port 250℃; detector 260℃; split ratio 10:1; injection volume 2μl; carrier gas flow rate 3.0ml / min; the gas chromatogram of the reference solution is shown in Figure 6; as shown in Figure 6, using the method of Comparative Example 1, dodecanol and 2-ethylhexanoic acid cannot be completely separated (only one sample peak can be detected), and this method is not suitable for simultaneous detection of dodecanol and 2-ethylhexanoic acid.

Claims

1. A method for detecting the impurity content in poly-L-lactic acid, characterized in that, The impurities are dodecanol and 2-ethylhexanoic acid; The method for detecting impurities in poly-L-lactic acid includes the following steps: (1) Preparation of test solution: The poly-L-lactic acid sample was dissolved in dichloromethane and diluted to volume to prepare the test solution; (2) Gas chromatography detection: Inject the test solution from step (1) into the gas chromatograph, record the chromatogram, and calculate the content of dodecanol and 2-ethylhexanoic acid according to the external standard method; The gas chromatography detection conditions are as follows: the chromatographic column is a capillary column with polyethylene glycol as the stationary phase; the column temperature is 135~155℃; the carrier gas is nitrogen, and the flow rate is 0.7~0.9 ml / min; the injection port temperature is 240~260°C; the detector temperature is 270~290°C; the injection method is split injection with a split ratio of 10:1; and the injection port pressure is 75 kPa.

2. The method for detecting impurities in poly-L-lactic acid according to claim 1, characterized in that, Step (1) Each 1 ml of the test solution contains 9-11 mg of poly-L-lactic acid sample.

3. The method for detecting impurities in poly-L-lactic acid according to claim 1, characterized in that, The chromatographic column used was a DB-WAX, 30m × 0.32mm, 0.5μm.

4. The method for detecting impurities in poly-L-lactic acid according to claim 1, characterized in that, In step (2), the injection volume into the gas chromatograph is 1.0 μL.

5. The application of the method for detecting the impurity content in poly-L-lactic acid according to any one of claims 1 to 4 in evaluating the quality of poly-L-lactic acid.

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